Fluid ejection printing devices, such as inkjet printers, print a printing fluid onto a page by ejecting droplets of the fluid onto a printing medium. Some fluid ejection printing devices print by producing a continuous stream of printing fluid droplets, for example, with a piezoelectric device, and then selectively deflecting the individual droplets to print a desired pattern of droplets onto the printing medium. Other fluid ejection printing devices, known as “drop-on-demand” devices, selectively eject drops of printing fluid, rather than continuously. Some devices utilize piezoelectric elements to trigger the ejection of printing fluid via a change in ejection chamber volume, while others use electrically resistive elements to thermally vaporize a component of the printing fluid, thereby selectively generating a bubble to drive printing fluid out of each orifice.
Thermal fluid ejection printing devices typically include an array of precisely formed nozzles (typically having a diameter between approximately 8 and 60 microns) located on a nozzle plate and attached to a printhead substrate. The substrate includes an array of firing chambers that receive printing fluids from one or more printing fluid reservoirs. Each chamber has a thin-film resistor, which may be referred to as a “firing resistor”, located opposite the nozzle. Printing fluid collects between the nozzle and the firing resistor for ejection through the nozzle. The substrate and nozzle plate are held and protected by an outer packaging, sometimes called a print cartridge. The total assembly may be referred to as a printhead. The firing of printing fluid droplets is typically controlled via a microprocessor. Upon energization of the firing resistor, a bubble of vaporized printing fluid components forms on the resistor, thereby expelling a droplet of printing fluid through the nozzle.
Many different types of printing fluids are known, including non-curable and curable printing fluids. Conventional thermally-ejectable printing fluids are generally aqueous-based and are non-curable. Therefore, the fluids tend to be relatively slow drying, and susceptible to smearing and color running during drying. In contrast, curable printing fluids offer the advantage of fast, almost instantaneous, drying times, thereby allowing a printed item to be handled almost immediately after printing. Instantaneous curing also enables the use of a much broader range of substrates, such as non-porous substrates, which do not absorb the ink. Examples include, but are not limited to, glass, plastic, metal, and many plastic coated paper products.
Generally, curable printing fluids include a polymerizable component that is cured by exposure to an energy source, such as UV light, heat, an electron beam, etc., after printing. Curable printing fluids also may help to reduce crusting or clogging of the printhead by remaining in the liquid phase inside of the printhead, thereby reducing servicing requirements.
However, current curable fluid ejection printing fluids may suffer various drawbacks. For example, conventional curable fluid ejection printing fluids may not be printable via thermal ejection, and therefore may require the use of more expensive and maintenance intensive piezoelectric printheads. Additionally, some curable printing fluids may include organic solvents such as methyl ethyl ketone in which the curable components are dissolved. Such solvents may require additional equipment and care for safe evaporation and disposal.